Die separation, or dicing, by sawing is the process of cutting a thin film microelectronic substrate into its individual read/write recording devices with a rotating circular abrasive saw blade. This process has proven to be the most efficient and economical method in use today. It provides versatility in selection of depth and width (kerf) of cut, as well as selection of surface finish, and can be used to saw either partially or completely through a wafer or substrate.
Wafer dicing technology has progressed rapidly, and dicing is now a mandatory procedure in most front-end thin film packaging operations. It is used extensively for separation of die on thin film integrated circuit wafers.
Dicing thin film wafers by sawing is an abrasive machining process similar to grinding and cutoff operations that have been in use for decades. However, the size of the dicing blades used for die separation makes the process unique. Typically, the blade thickness ranges from 0.6 mils to 500 mils, and diamond particles (the hardest known material) are used as the abrasive material ingredient. Because of the diamond dicing blade's extreme fineness, compliance with a strict set of parameters is imperative, and even the slightest deviation from the norm could result in complete failure.
The diamond blade is a cutting tool in which each exposed diamond particle comprises a small cutting edge. Three basic types of dicing blades are available commercially:
Sintered Diamond Blade, in which diamond particles are fused into a soft metal such as brass or copper, or incorporated by means of a powdered metallurgical process.
Plated Diamond Blade, in which diamond particles are held in a nickel bond produced by an electroplating process.
Resinoid Diamond Blade, in which diamond particles are held in a resin bond to create a homogeneous matrix.
Thin film wafer dicing is dominated by the plated diamond blade, which has proved most successful for this application.
Increasing use of more expensive and exotic materials, coupled with the fact that they are often combined to produce multiple layers of dissimilar materials, adds further to the dicing problems. The high cost of these substrates, together with the value of the circuits fabricated on them, makes it difficult to accept anything less than high yield at the die-separation phase.
Thin film wafers are of a standardized size, and thus, the number of die that can be cut from each wafer is limited. To maximize the amount of wafer space that can be used for circuitry, and thus the die yield per wafer, the area cut away during slicing must be minimized. This can be accomplished only by using thinner blades and by elimination of yield loss due to deviation of the blade from the desired cut path.
One category of component created by thin film processing is the tape head. Many heads (such as hard disk recording heads and some tape heads) do not use closures, so they are relatively easy to slice. However, most conventional tape heads use closures. FIG. 1 depicts one such tape head 100. The head 100 consists of a pair of head portions 102, each having a closure 104 that engages the tape 106 as it passes over the head 100.
For those heads that use closures, a problem arises during slicing by state of the art methods. To maximize yield, the cut is made through the wafer 202 such that it shaves off one edge of the closure 104. See FIG. 2. Because the blade engages more material on one side of the blade than the other, the blade becomes distorted, causing the blade to stray from the desired cut path and destroy die.
Cutting the wafer along side the closure rather than through the edge of the closure is not desirable for cutting rows from the wafer because of the typically high margin of error during sawing. By moving the saw path closer to the circuitry, the blade is more likely cut into the read/write circuitry, rendering the die unusable. The only remedy under this traditional method of cutting would be to increase the size of each row on the wafer to compensate for blade deviation or to accommodate a thicker blade. Either way, the end result would be an undesirable decrease in yield.
FIG. 3 depicts a prior art attempt at reducing blade distortion. As shown, a stiffener 300 is coupled to the non-wafer-contacting portion of the blade 200 to add to the resiliency of the blade 200. While this solution does remedy blade distortion to a degree, it does not eliminate the yield loss completely, as some distortion still occurs, with the resulting deviation from the cut path and circuit destruction.
It would be desirable to achieve the aforementioned benefits using conventional, and therefore, less expensive blades. It would also be desirable to use a thinner blade to allow a higher yield per wafer. It would also be desirable to decrease the error rate caused by deviation of the blade during sawing